We have demonstrated that endothelial cells (EC) are highly resistant to the injurious effects of acute and chronic hypoxia and have theorized that in EC, as in other hypoxia tolerant organisms or tissues, multiple factors contribute to their remarkable hypoxia tolerance. Among these potential factors are plasmalogens, a subset of "vinyl ether" phospholipids that are found within cellular membranes, constitute .18% of the total phospholipid mass in humans and have been identified as potent endogenous antioxidants. We have developed substantial evidence that plasmalogens exist in human and bovine pulmonary artery EC (HPAEC and BPAEC) and human brain microvascular EC and that increased plasmalogen levels correlate with resistance of human EC to the injurious effects of hypoxia and reactive oxygen species (ROS). Plasmalogen protection appears stress specific in that HPAEC with increased levels of plasmalogen are not protected against other common cellular stresses, such as heat shock or glucose deprivation. These findings suggest that plasmalogens can contribute to the protection of EC against specific cellular stresses; to investigate this hypothesis further, we will: 1) Define the role of plasmalogens in human EC survival during hypoxia: by establishing a relationship between plasmalogen levels and cell damage during exposure to hypoxia through modulation of plasmenylcholine content; by determining plasmalogen loss in normoxia and during exposure to hypoxia; by determining chemical breakdown, metabolic products of plasmalogens and/or plasmalogen-dependent eicosanoid products in normoxia and during hypoxia to determine if plasmalogens act as scavengers of ROS or as precursors for second messengers. 2) Define the stress-specific protection of increased human EC plasmalogen content: by comparing cell damage during exposure to hypoxia and other cellular stresses (exposure to ROS, change in redox potential, increased temperature, glucose depletion, etc): by determining the association between plasmalogens and cellular oxidants, cellular oxidases and antioxidants. Once the biochemistry of plasmalogens in EC has been clarified, studies to determine their biological importance can be undertaken. [unreadable] [unreadable]